With USB now serving as a common connector for portable devices, such as notebooks, tablets, PDAs, and cell phones, dedicated chargers are no longer a sole or main source for charging many portable devices. For example, auto manufacturers around the world are increasingly integrating USB into the vehicle console to serve as both a data connection and as a universal charging interface for any USB-compatible device that a driver may wish to charge while in the auto. In addition, generic wall chargers are widely available to supply charge to any device having a USB port. In some cases, the USB port may be optimized for only charging, which is known as a Dedicated Charging Port or DCP. A DCP reduces the cost of USB-based charging by implementing only those components required for charging devices.
The range of typical output currents for different charging sources may be up to about several Amperes (A). Charging time is dependent upon the charging current, so that the more current a device can draw, the faster it can charge. By supplying up to 1.5 A charging current, a DCP port can significantly reduce device charging time compared to chargers limited to 500 mA or less.
However, one issue of concern for charging a device from an unknown charging source is that the output current may be different for different charging sources, such as different USB chargers. When a device is charged by an unknown charging source, the portable device may have no information as to the amount of current that can be delivered from the charging source. Instead, the portable device may be set to blindly assume that a particular value of current can be delivered from the USB charging source. Even in cases where the portable device recognizes the type of charger, it may attempt to draw current at levels very different from that supplied by the charger. In some cases, the portable device may be capable of determining that a USB charging source is a DCP or an Accessory Charger Adapter (ACA), from which it may be assumed that the range of available current is between 500 mA to 1.5 A, in keeping with present day standards. In such cases, the portable device may either assume that a minimum or maximum amount of current can be supplied, depending on how aggressively the device is arranged to charge the battery. For example, the portable device may be set to draw large currents under the assumption that a maximum amount of current can be delivered from the charging source, and may then monitor the charging process once a large current is drawn. In some cases, without knowledge of the actual charging current capability of the charger, the portable device may begin to blindly draw 1.5 A current to charge its battery, even when the charging source can only provide 500 mA of charging current. This may lead to collapse of the charging source's voltage, requiring the circuitry in the portable device to turn off or the charger to turn down, which may potentially harm the battery or trip circuitry in the portable device or charging source.
On the other hand, if the portable device is blindly set to draw 500 mA, the charge time may be unnecessarily lengthened if the charging source is capable of providing a higher current. In addition, the power made available to the system may be unnecessarily limited by a low current setting.
It is with respect to these and other considerations that the present improvements have been needed.